Effect of bacterial exopolysaccharide on the physical properties of acid milk curd by lactic acid fermentation

Abstract

Exopolysaccharide (EPS) is an extracellular slime polysaccharide from bacteria and one of EPS produced by Alcaligenesfaecalis var. myxogenes strain 10C3 which found by Harada for the first time in 1965. In this study, it was used Lactobacillus delbrueckii subsp. bulgaricus B-5b, which obtained from Japan Milk Product Technology Association, Tokyo, Japan. During the course of the investigation, the culture was routinely propagated in 10% RSM. The RSM was added with 0, 0.5 and 1% of EPS, autoclaved at 121°C for 15 min and tempered to 37°C prior to inoculation. A 0,1% inoculum was added to the RSM and the culture was allowed to incubate at 37°C overnight. Milk curd investigated toward growth curve of cell bacteria numbers, pH, acidity, viscosity, rheometric properties. The result indicated that increasing EPS concentration cause of increases the pH and the pH of milk increases its viscosity perhaps by swelling of casein micelles, but a more drastic pH decreases causes the viscosity to increase, which is caused by aggregation of casein. On the other side, increasing the EPS concentration decreases acidity as expected. It is well established that milk which has been heated at a temperature above 70°C has a longer coagulation time and forms a weaker curd than the original unheated milk.

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